Protective films containing compatible plasticizer compounds useful in polarizing plates for displays and their method of manufacture

ABSTRACT

Polymer films comprising plasticizer compounds represented by Structure 1 as described in the specification are useful as protective films in polarizing plates for display applications. Methods of manufacturing such polymer films and polarizing plates are also disclosed.

FIELD OF THE INVENTION

The present invention relates to polymer films comprising plasticizersuseful in polarizing plates and display applications. In particular, theinvention relates to the use of plasticizer compounds comprising esterlinkages that are not directly bonded to an aryl group, and in which atleast one ester linkage is directly or indirectly bonded to an alicylicring.

BACKGROUND OF THE INVENTION

The proliferation of flat panel displays into increasing numbers ofapplications places higher demands on the performance of all displaycomponents. Flat panel displays based on liquid crystal switching modesand electroluminescent technology both depend on the use of polarizingplates to improve the image quality. With the increasing penetration offlat panel displays into mobile and outdoor application comes the demandfor improved environmental stability of all components.

One component of displays that have long been known to have severerestrictions on environmental durability, in particular with respect toexposure to elevated temperature and humidity, are polarizing plates.Polarizing plates are multi-layer structures comprising an orientedpolarizing film. Polarizing films require a protective covering tomaintain stability of the polarizing film. Conventionally, protectivepolymer films 1 have been laminated to both faces of a polarizing film 2as shown in FIG. 1. The most commercially successful class of polarizingfilms comprises oriented polyvinyl alcohol (PVA) that has been dyed toprovide polarizing activity in the visible light spectrum. Theprotective films are required to be optically transparent, dimensionallystable, mechanically tough, and chemically compatible with polarizingfilms. The most commercially successful of these protective films hasbeen cellulose triacetate (commonly known in the polarizer industry astriacetyl cellulose or TAC), although other polymers may be used.

For the purposes of this invention the following terms are defined:

A “polarizing film” is defined herein as a self-bearing oriented polymerfilm with associated addenda that performs the function of polarizinglight. For example, oriented PVA film that has been dyed by complexationwith dichroic organic compounds or iodine and cross-linked with borate,including ancillary addenda, is an effective polarizer film. Henceforthherein it is understood that the term “dye” includes dichroic organiccompounds and iodine, except as otherwise specified.

A “protective film” is defined herein as a self-bearing polymer filmwith associated addenda, such as plasticizers, UV absorbers,stabilizers, etc., that is laminated, adhered to, coated, or otherwiseapplied onto the polarizing film to provide protection for thepolarizing film. Protective functions can include providing stability interms of mechanical, optical, chemical, or other properties andresistance to environmental degradation. The durability of polarizingplates is conventionally measured based on retention of theirpolarization efficiency and light-transmission performance when exposedto elevated temperature and/or humidity environments for extended timeperiods.

A “protective film” can comprise part of a composite film including, forexample, a carrier layer. A “polarizing plate” is defined herein as themultilayer polymer film structure consisting of at least one polarizingfilm and at least one protective film. The invention is particularlyadvantageous when the protective film is the first self-bearing filmcontiguous to the polarizing film in a polarizing plate.

Previous approaches have been described which attempt to improve theenvironmental durability of polarizing plates. For the most part theseefforts have focused on controlling the moisture content and moisturepermeability of the protective films in the polarizing plate (See, forexample, US 20020192397A1, US 20020162483A1, and US 20030037703A1).These approaches have attempted to control the moisture permeationproperties through the use of high levels of organic compounds known toplasticize the protective film. For the purposes of this invention aplasticizing compound or “plasticizer” is defined as a compound that ischemically compatible with the polymer and reduces brittleness orimparts improved flexibility and elongation to the film.

In support of the present invention, intensive study was undertaken todetermine the key factors compromising the durability of polarizerplates under environmental stress, i.e., elevated temperature and/orhumidity. This study has shown that acceptable moisture permeation ofthe protective film, as defined for example in US patent application20020192397A1, allows polarizer plates to rapidly achieve moistureuptake equilibrium. The key factor contributing to long-term failure ofpolarization efficiency and light transmission performance of polarizerplates was determined to depend on the release of active chemicalspecies, particularly those that are mobile. In particular, thesespecies were found to be related to the breakdown products ofplasticizer and other protective film components. These findings aresupported by prior work as found, for example, in: Shinigawa et al.“Investigation of the Archival Stability of Cellulose Triacetate Film:The Effect of Additives to CTA Support,” Polym. Conserv., 105 (1992),138-150; and Ram et al. “The Effects and Prevention of the ‘VinegarSyndrome’,” J. Imaging Sci. and Tech., 38 (1994), 749-761, all herebyincorporated by reference.

Prior attempts to improve the durability of polarizer plates have beendescribed. US patent application 20020192397A1 discloses the use ofelevated levels of phosphate ester plasticizers to control the moisturepermeability of the protective film. However, as noted by Ram et al. andShinigawa et al., phosphate ester plasticizers release strongly acidiccompounds upon exposure to elevated humidity. In addition, chemicallyactive hydroxy arenes, such as phenols, are released.

The use of a small-molecule basic compound (tributyl amine) is alsodisclosed in US 20020192397A1 to reduce the odor of acetic acid in TACprotective films. Small-molecule basic compounds are not preferred,however, as they readily migrate into the polarizer film and arereactive toward the polarizer dye components.

The use of ester compounds that can release chemically active hydroxyarenes, such as phenol, is also not preferred. The current study hasshown that undesirable reaction with iodine in the polarizer film toproduce iodophenols occurs in polarizer plates that have been subjectedto elevated temperature and humidity when hydroxy arene esterplasticizers are employed. The reactivity of hydroxy arenes towardhalogens is well known, as described by Morrison, R. T. and Boyd, R. N.,Organic Chemistry, 3^(rd) Ed., Allyn and Bacon, Boston, 1976, pp.801-802, hereby incorporated by reference.

US 20020162483A1 and U.S. Pat. No. 5,753,140 disclose the use ofelevated levels of aromatic ester plasticizers to control moisturepermeability and moisture content in protective films for polarizerplates. Such compounds release strongly acidic compounds and/orchemically active hydroxy arenes upon exposure to elevated humidity. USpatent application 20030037703A1 discloses the use of elevated levels ofmonocarboxylic acid esters of polyhydric alcohols as plasticizers tocontrol moisture permeability of protective films for polarizer plates.Due to the use of esters of monocarboxylic acids, again elevatedhumidity conditions lead to the production of mobile acidic compounds.

In the cases described above (US 20020192397A1, US 20020162483A1, and US20030037703A1), the acidic species and hydroxy arenes produced have thepotential to readily migrate through the polarizer plate structure.Strongly acidic species can participate in the degradation of theprotective films, the adhesion interface to the polarizing film, andmost critically, the organic dyes in the polarizing film. Interaction ofthe dyes in the PVA polarizing film with such reactive species canproduces significant hue shift contributing to degradation of thepolarizer plate performance.

In addition, in the cases described above (US 20020192397A1, US20020162483A1, US 20030037703A1) high levels of these compounds (>15% byweight) are incorporated into the polymer lamination films in order toprovide significant control of moisture permeability and moisturecontent. These high levels are undesirable as they lead to unacceptableloss of toughness by the protective film through reductions in polymermodulus (Handbook of Plasticizers, G. Wypych, ed., ChemTec Publishing,NY, 2004, Chap. 10).

SUMMARY OF THE INVENTION

The present invention is directed to a self-bearing protective filmcontaining at least one compound selected from a class of compoundshaving non-aryl ester linkage which compounds are represented by thefollowing Structure I:

wherein:

R¹ and R² are both non-aryl groups; n is 2 or more; and at least one ofR¹ and R² comprise at least one cycloalkyl group. The “n” multiple R²groups may be the same or different from one another.

A non-aryl group, in the above Structure I, is defined as a group thatdoes not provide a direct bond between the —C(═O)O— linkage in StructureI (hereafter the “ester link”) to an aromatic moiety. One or morearomatic or aryl groups may optionally be present elsewhere in thechemical structure of R¹ and R² as long as such a group is not directlybonded to the ester link shown in Structure I, preferably all esterlinks present in the compound.

In one embodiment of the invention, the R¹ and R² non-aryl groups,respectively, are residues of an alcohol and carboxylic acid that reactto form the ester link, such that the ester link is not directly bondedto an aryl moiety.

In one embodiment of the invention, the self-bearing film is used as aprotective film for a polarizing film in a polarizing plate, wherein thepolarizing film comprises dye-doped polyvinyl alcohol useful in displayapplications. The use of the present plasticizer compoundsadvantageously provides an unexpectedly significant increase inenvironmental durability of the polarizing film.

In another embodiment of the invention, the incorporation of oligomericand polymeric low-mobility basic compounds in the protective film, inaddition to the plasticizer compounds, provides a further significantincrease in environmental durability.

Sill another embodiment of the invention is directed to a method ofmaking the protective film of the present.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a polarizing plate that shows theconfiguration of layers consisting of protective films on either side ofa polarizing film.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be attained by a polymer film comprising anester compound of a non-aromatic polycarboxylic acid and one or moremonohydric alcohols. Functions of the non-aromatic ester compounds toprovide materials of increased environmental durability are furtherclarified herein.

As indicated above, the polymeric protective film that providesincreased environmental durability is comprised of a compositioncontaining at least one compound of a class of ester compoundsrepresented by the following Structure I:

wherein:

R¹ and R² are both non-aryl groups;

n is an integer of 2 or more; and

R¹ and/or R² comprise (in whole or part) at least one cycloalkyl group.

As evident by Structure I, the —(C═O)O— ester link is linked to R¹ bythe carbonyl carbon of the carboxyl group and to R² by the oxy groupattached to the carboxy group. Preferably, there are no aryl groupsdirectly bonded to any ester linkage in the compound of Structure I.

In a preferred embodiment, the non-aryl groups R¹ and R² substituted orunsubstituted organic groups independently selected from the groupconsisting of alkyl, alkenyl, alkynyl, cycloalkyl, and cycloalkenyl, solong as at least one or more groups in R¹ and/or R² groups comprise acycloalkyl group (in whole or part). One or more aromatic functionalgroups may optionally be present as part of the chemical structure of R¹or R² but, as mentioned above, the one or more aromatic functionalgroups may not be directly bonded to the carbonyl carbon or oxy atom(attached to the carboxyl group) in the ester link —(C═O)O—. Heteroatomssuch a oxygen, nitrogen, and sulfur may be present as part of thechemical structure of R¹ or R², but the heteroatoms are preferably notdirectly bonded to the carbonyl carbon or oxy atom.

Examples of the R¹ and R² organic groups include such alkyl groups asethyl, propyl, butyl, etc.; alkenyl groups such as ethylenyl,propylenyl, etc.; alkynyl groups such as propynyl, etc.; cycloalkylgroups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,methylcyclohexyl, etc.; alkyl cycloalkyl, alkylene cycloalkyl, etc.; andheterocyclic groups, which organic groups may be substituted. Theorganic group described above may be substituted to contain heteroatomsas a portion of the group (for example: oxygen to imply alkyl ethers,tetrahydrofurans, etc.; sulfur to imply alkyl thioethers, or nitrogen toimply saturated heterocycles such as piperidinyl etc.). The heteroatomis preferably not directly bonded to the carboxylic acid. The organicgroup described above may contain additional substituent groups (forexample, a phenyl group, a hydroxyl group, an alkyl group, a halogengroup, etc.) Aromatic rings that may form a substituent on the organicgroups of the non-aryl ester can include, for example, a phenyl ring, anaphthalene ring, or an anthracene ring.

In a particularly preferred embodiment, R¹ and/or R² comprise acyclohexyl or cyclopentyl group.

In general, when reference in this application is made to a particularmoiety or group it is to be understood that such reference encompassesthat moiety whether unsubstituted or substituted with one or moresubstituents (up to the maximum possible number). For example, “alkyl”or “alkyl group” refers to substituted or unsubstituted alkyl, while“phenyl group” refers to a substituted or unsubstituted phenyl (with upto six substituents). Generally, unless otherwise specifically stated,substituent groups usable on molecules herein include any groups,whether substituted or unsubstituted, which do not destroy propertiesnecessary for plasticizing utility. Examples of substituents on any ofthe mentioned groups can include known substituents, such as: chloro,fluoro, bromo, iodo; hydroxy; alkoxy, particularly those “lower alkyl”(that is, with 1 to 12 carbon atoms, for example, methoxy, ethoxy;substituted or unsubstituted alkyl, particularly lower alkyl (forexample, methyl, trifluoromethyl); thioalkyl (for example, methylthio orethylthio), particularly either of those with 1 to 12 carbon atoms;substituted or unsubstituted alkenyl, preferably of 2 to 12 carbon atoms(for example, ethenyl, propenyl, or butenyl); substituted andunsubstituted aryl (within the limits of Structure I), particularlythose having from 6 to 20 carbon atoms (for example, phenyl); andsubstituted or unsubstituted heterocyclic and (within the limits ofStructure I) heteroaryl, particularly those having a 5 or 6-memberedring containing 1 to 3 heteroatoms selected from N, O, or S (forexample, pyridyl, thienyl, furyl, pyrrolyl); and other groups known inthe art. Further, with regard to any alkyl group or alkylene group, itwill be understood that these can be branched or unbranched and includering structures. As indicated above, the preparation of the non-arylester compounds involve the reaction product on alcohol and a carboxylicacid. In one embodiment of the invention, the R¹ and R² non-aryl groups,respectively, in the above Structure I, are residues, respectively, ofan alcohol and carboxylic acid that react to form the ester link, suchthat the ester link is not directly bonded to an aryl moiety.

In one preferred embodiment, the carboxylic acid is a non-arylpolycarboxylic acid (a compound having a plurality of, namely two ormore, carboxylic acid groups on an organic moiety) that is representedby the following Structure II:R¹—(COOH)_(n)  (II)wherein:

R¹ is the same non-aryl group as described above, and n is an integer ofnot less than 2, preferably 2.

Again, one or more aromatic functional groups may be present as part ofthe chemical structure of R¹, but the one or more aromatic functionalgroups may not be directly bonded to the carbonyl carbon. In oneembodiment, the polycarboxylic acids have pKa greater than 3, preferablygreater than 3.5. Most preferred are polycarboxylic acids having pKagreater than 4.

Examples of polycarboxylic acids include, but are not limited to, thefollowing: malonic acid, methylmalonic acid, butylmalonic acid,dimethylmalonic acid, succinic acid, methylsuccinic acid,dimethylsuccinic acid, 2-ethyl-2-methylsuccinic acid, glutaric acid,2,4-dimethylglutaric acid, adipic acid, methyladipic acid,tetramethylhexanedioic acid, pimelic acid, suberic acid,1,10-decanedicarboxylic acid, sebacic acid, hexadecanedioic acid,tricarballylic acid, methyltricarballylic acid,1,2,3,4-butanetetracarboxylic acid, fumaric acid, citraconic acid,beta-hydromuconic acid, hexafluoroglutaric acid, tartaric acid, citricacid, diglycolic acid, tetrahydrofuran-2,3,4,5-tetracarboxylic acid,3,3′-thiodipropionic acid, 4-ketopimelic acid,1,1-cyclopropanedicarboxylic acid, 1,2-cyclobutanedicarboxylic acid,1,2-cyclopentanedicarboxylic acid, 3,3-tetramethyleneglutaric acid,camphoric acid, 1,1-cyclohexanediacetic acid,1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, 1,3-adamantanedicarboxylic acid,5-norbornene-2,3-dicarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid,1,2,3,5-cyclohexanetetracarboxylic acid,1,2,4,5-cyclohexanetetracarboxylic acid,1,2,3,4-cyclobutanetetracarboxylic acid,1,2,3,4,5,6-cyclohexanehexacarboxylic acid.

The alcohols, preferably monohydric, that may be used for thepreparation of the non-aryl ester in the present invention are limitedby the requirement that the hydroxyl functional group is not attached toan aromatic group. Monohydric alcohols that may be used includealiphatic and cyclic alcohols. The aliphatic and cyclic alcohols maycontain additional substituent groups (for example, a phenyl group, analkyl group, a halogen group, etc.).

Preferred examples of the alcohols include aliphatic straight chain orbranched chain organic groups having a carbon atom number of preferably1 to 32, more preferably from 1 to 20, and most preferably 1 to 16.Cyclic monohydric alcohols include monocyclic, bicyclic, or tricyclicring structures having a carbon atom number of preferably 3 to 20, morepreferably 4 to 14, and most preferably 5 to 8. Such monohydric alcoholsmay also contain heteroatoms as a portion of the chain or ring (forexample: oxygen to imply alkyl ethers, tetrahydrofurans, etc.; sulfur toimply alkyl thioethers, or nitrogen to imply monohydroxy substitutedheterocycles such as N-methylpiperidinol, etc.). The heteroatompreferably is not be directly bonded to the hydroxyl group.

Examples of monohydric alcohols that may be used include, but are notlimited to, the following: methyl alcohol, ethyl alcohol, propanol,butanol, pentanol, hexyl alcohol, heptanol, octanol, dodecanol,2-propanol, 2-octanol, 3-methyl-2-butanol, 2-methyl-2-propanol,4-penten-1-ol, cyclopropanemethanol, cylclobutanol, cyclobutanemethanol,cyclopentanol, 3-cyclopentyl-1-propanol, cyclohexanol,methylcyclohexanol, cyclohexylmethanol, cyclohexylethanol,4-ethylcyclohexanol, cycloheptanol, cyclooctanol, norborneol,decahydronaphthol, cyclohexenol, 6-chloro-1-hexanol, heptafluorobutanol,2-(2-ethoxyethoxy)ethanol, 2-(cyclohexyloxy)ethanol, glycidol,hydroxytetrahydrofuran, tetrahydropyran-2-methanol,tetrahydropyran-4-ol, 2-methylthioethanol, 2-hydroxyethylpyrrolidine,4-hydroxy-1-methylpiperidine.

The molecular weight of the non-aryl ester compounds used in theinvention is not specifically limited, but is preferably from 250 to1500, and more preferably from 300 to 750. The non-aryl ester compoundsof relatively higher molecular weight may be preferable with respect tothe property of lower sublimation during polymer casting, whereas thenon-aryl ester compounds of relatively lower molecular weight may bepreferable with respect to the property of improved miscibility withfilm polymers including cellulose acetate.

The alcohols for the preparation of the non-aryl polycarboxylic estersused in the present invention may be used singly or in a mixture of twoor more kinds thereof. It is especially preferred that all thecarboxylic acid groups of the non-aryl polycarboxylic acid be esterifiedsuch that no free carboxylic acid functional groups remain when added tothe polymer phase for the protective film.

As indicated above, the non-aryl ester compounds used in the inventioncontain a cycloalkyl ring in the molecule. Such cycloalkyl ring may be afunctional group of either one or both of the non-aryl polycarboxylicacid or the monohydric alcohol that can be used in preparing thecompounds. An especially preferred non-aryl ester would contain at leastone cyclohexyl ring.

Examples of non-aromatic polycarboxylate esters in the invention areexemplified by the compounds described in DE20021356U1 page 3; line 25through page 41; line 12 the disclosures of which are incorporated byreference herein. In addition, examples of the non-aromaticpolycarboxylate esters in the invention are exemplified below but arenot limited thereto.

The plasticizer is preferably contained in the film in an amount of0.01% to 30 weight %, preferably in the amount of 5% to 15 weight %,most preferably in the amount of 10% to 15%.

The protective film generally may contain one or more additionalplasticizers other than those of the present invention, preferably inlesser amounts by weight. Examples of such other plasticizers includephosphate esters such as triphenyl phosphate, biphenylyl diphenylphosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyldiphenyl phosphate, trioctyl phosphate, and tributyl phosphate; andphthalate esters such as diethyl phthalate, dimethoxyethyl phthalate,dimethyl phthalate, and dioctyl phthalate; glycolic acid esters such astriacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalylethyl glycolate, and methyl phthalyl ethyl glycolate.

Another embodiment of the invention comprises the incorporation ofoligomeric and polymeric low-mobility basic compounds in the protectivefilm, in addition to the plasticizer compounds, to provide a furthersignificant increase in environmental durability. Low mobility is hereindefined as being exemplified by polymer film components with limitedtendency those migrate due to compatibility and diffusivity. Suchcompounds are believed to function to scavenge any acids that form inthe film. Examples of oligomer and polymeric low-mobility basiccompounds are exemplified below, but are not limited thereto:

Poly(4-vinylpyridine) and poly(2-vinylpyridine)

Poly(acrylonitrile-co-butadiene), amine terminated

Poly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine]

Poly(1,2-dihydro-2,2,4-trimethylquinoline)

Polyethyleneimine, high molecular weight

Polyethyleneimine, epichlorohydrin modified

Polyethylenimine, 80% ethoxylated

Poly(9-vinylcarbazole)

Poly(vinyl chloride-co-1-methyl-4-vinylpiperiazine)

Poly(4-vinylpyridine-co-butyl methacrylate)

The low-mobility basic compound is preferably contained in the film inan amount of less than 5 weight %, preferably in the amount of 0.01% to2 weight %, most preferably in the amount of 0.1% to 1%.

Protective films preferably also contain an ultraviolet absorber toprovide a sharp UV cut-off (wavelength value) in the transmittancecurve. In accordance with specific embodiments of the invention,ultraviolet light absorbing compounds preferably comprise adibenzoylmethane, hydroxyphenyl-s-triazine, hydroxyphenylbenzotriazole,formamidine, benzophenone, or benzoxazinone compound and derivativesthereof. Additional possible UV absorbers which may be employed includesalicylate compounds, such as 4-t-butylphenylsalicylate; and[2,2′-thiobis-(4-t-octylphenolate)]-n-butylamine nickel(II). Suchultraviolet light absorbing compounds are themselves known, and havebeen described for use in various polymer films. Preferred arederivatives of dibenzoylmethane, hydroxyphenyl-s-triazine andhydroxyphenylbenzotriazole compounds. Combinations of UV absorbertechnologies may be employed as disclosed in copending commonly assignedUS patent application publication US 20030080326A1, hereby incorporatedby reference herein.

The protective film used in the present invention may optionally containparticles of an inorganic or organic compound to provide surfacelubrication. Examples of the inorganic compound include silicon dioxide,titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate,talc, clay, calcined kaolin, calcined calcium silicate, hydrate calciumsilicate, aluminum silicate, magnesium silicate, and calcium phosphate.Preferred are silicon dioxide, titanium dioxide, and zirconium oxide,and especially silicon dioxide. Examples of the organic compound(polymer) include silicone resin, fluororesin and acrylic resin.Preferred is acrylic resin as disclosed in copending commonly assignedUS patent application publication US 20030180528A1, hereby incorporatedby reference herein.

Examples of preferred polymers employable for use as the polymeric phasein the protective film of the present invention include polyesters(e.g., polyethylene terephthalate and polyethylene-2,6-naphthalate);cellulose esters (e.g., cellulose diacetate, cellulose triacetate,cellulose acetate propionate, and cellulose acetate butyrate);polyolefins (e.g., polypropylene and polyethylene); acrylic resins(e.g., polymethyl methacrylate); polycarbonate esters (e.g.,polycarbonate); norbornene resins, and the like.

In one preferred embodiment, the protective film of the invention is inthe form of a self-bearing polymer film wherein the polymer is acellulose ester such as a cellulose acetate, particularly cellulosetriacetate. As the cellulose triacetate, known materials can beemployed. The combined acetic acid acetyl value of cellulose triacetatepreferably is in the range of 35% to 70% weight, especially in the rangeof 55% to 65% weight. The weight average molecular weight of celluloseacetate preferably is in the range of 70,000 to 200,000, especially80,000 to 190,000. The polydispersity index (weight average divided bynumber average molecular weight) of cellulose acetate is in the range of2 to 7, especially 2.5 to 4. Cellulose acetate may be obtained fromcellulose starting materials derived from either wood pulp or cottonlinters. Cellulose acetate may be esterified using a fatty acid such aspropionic acid or butyric acid so long as the acetyl value satisfies thedesired range.

The protective film may have a thickness ranging from 5 to 200 microns,preferably 15 to 100 microns, more preferably about 20 to 80 microns.

In a preferred embodiment, the protective films exhibit an in-planeretardation ranging from 0.1 to 15 nm, an out-of-plane retardationranging from −10 to −100 nm, and total haze less than 1 percent. Suchprotective films may additionally exhibit an equilibrium moisturecontent at 25 C and 50% RH of less than 5% by weight.

Protective films according to the present invention may be prepared by avariety of methods. In one preferred embodiment, such films are preparedby utilizing a solvent coating or casting method. Details of the solventcoating method are described in copending commonly assigned US patentapplication publication 2003/0215582A1, the teachings of which arehereby incorporated herein by reference. The solvent casting method maycomprise the steps of: casting the polymer solution fed from a slit of asolution feeding device (die) onto a support and drying the cast layerto form a film. In a large-scale production, the method can beconducted, for example, by the steps of casting a polymer solution(e.g., a dope of cellulose triacetate) onto a continuously moving bandconveyor (e.g., endless belt) or a continuously rotating drum, and thenvaporizing the solvent of the cast layer. In a small-scale production,the method can be conducted for example, by the steps of casting apolymer solution fed from a slit of a solution feeding device on a fixedsupport having a regular size such as a metal plate or glass plate bymoving the device, and then vaporizing the solvent of the cast layer.

Any support can be employed in the solvent casting method, so long asthe support has the property that a film formed thereon can be peeledtherefrom. Supports other than metal and glass plates (e.g., plasticfilm) are employable, so long as the supports have the above property.Any die can be employed, so long as it can feed a solution at a uniformrate. Further, as methods for feeding the solution to the die, a methodusing a pump to feed the solution at a uniform rate can be employed. Ina small-scale production, a die capable of holding the solution in anappropriate amount can be utilized.

The polymer employed in the solvent casting method is required to becapable of dissolving in a solvent. Further a film formed of the polymeris generally required to have high transparency for application inoptical products. Furthermore, the polymer preferably has compatibilitywith the plasticizers. As the polymer employed in the solvent coating orcasting method, preferred is cellulose triacetate. However, otherpolymers including, but not limited to, polyesters, cellulose esters,polyolefins, acrylic resins, polycarbonate esters, or norbornene resinscan be employed so long as they satisfy the above conditions.

As another possible method for the formation of protective film, otherthan the solvent casting method, there can be mentioned the well knownextrusion molding method comprising the steps of mixing the polymer andthe addenda in a melt, and extruding the mixture. The method is usuallyapplied to polymers that cannot utilize the solvent casting method.

In another aspect of the present invention, the self-bearing film isused as a protective film for a polarizing film in a polarizing plate,typically wherein the polarizing film comprises dye-doped polyvinylalcohol useful in display applications. Any polarizing film can be used,however, including conventional films well known in the art. Asmentioned above, one type of polarizing film is produced by stretching afilm of polyvinyl alcohol (PVA) and then causing iodine to be adsorbedas a polarizing element on the resulting oriented film. Those polarizersmaking use of iodine as a polarizing element have good opticalperformance, displaying high photopic transmission and high polarizationefficiency. Another type of polarizing film, considered more durableunder conditions of high temperature and humidity, uses dichroic organicdyes as a replacement for iodine in the polarizers. Many examples ofdichroic organic dyes for polarizing films may be found in the patentliterature, for example: U.S. Pat. No. 5,310,509, U.S. Pat. No.5,340,504, U.S. Pat. No. 5,446,135, JP 2002296417, JP 2000329936, JP05273788, JP 63243166, EP 549342, U.S. Pat. No. 5,667,719, and thejournal literature such as Proceedings of the SPIE-Int. Soc. Opt. Eng.Vol. 2407, pp. 62-72, “Highly Durable Dyed Polarizer for Use in LCDProjections,” all of these hereby incorporated by reference with respectto the described polarizing film.

Polarizing films that make use of dichroic organic dye as a polarizingelement, although tending to have better durability against water andheat compared with polarizing films using iodine, tend to show increasedsensitivity to hue change in the presence of acidic species. It iscommon practice to use water-soluble azo dyes for the manufacture ofpolarizing films. Combinations of two or more dyes make it possible toproduce polarizing films dyed in various hues. It is common to usemultiple dyes with a high degree of dichroism to provide a neutral hueto the polarizing film.

Examples of dichroic dyes (Colour Index Generic Name) include, but arenot limited thereto, the following:

-   C.I. Direct Yellow 12, C.I. Direct Blue 202, C.I. Direct Red 31,    C.I. Direct Yellow 44, C.I. Direct Yellow 28, C.I. Direct Orange    107, C.I. Direct Red 79, C.I. Direct Blue 71, C.I. Direct Blue 78,    C.I. Direct Red 2, C.I. Direct Red 81, C.I. Direct Violet 51, C.I.    Direct Orange 26, C.I. Direct Red 247, C.I. Direct Blue 168, C.I.    Direct Green 85, C.I. Direct Brown 223, C.I. Direct Brown 106, C.I.    Direct Yellow 142, C.I. Direct Blue 1, and:    C.I. Direct Violet 9

C.I. Direct Red 81

Chemical Abstracts Registry Number 6300-50-1

Chemical Abstracts Registry Number 134476-95-2

Chemical Abstracts Registry Number 121227-50-7

C.I. Direct Blue 98

A process for the preparation of the protective film in the form of anoptical polymer film in accordance with one preferred embodiment of theinvention will now be explained in detail, in this case employingcellulose triacetate as the polymer phase for the film. In a mixingvessel, a solvent, cellulose triacetate and one or more plasticizersaccording to the present invention are placed, and cellulose triacetateis dissolved by stirring (under heating, if desired under pressure) toprepare a dope.

In another or second mixing vessel, a solvent and selection ofultraviolet (UV)absorbers, chemical stabilizers, and additionalplasticizers are placed, and are dissolved by stirring. In the case thatparticles to improve surface lubrication are added, the particles may beplaced in the resultant UV absorber containing solution and the mixtureis dispersed using a dispersing machine to prepare a dispersion. Anappropriate amount of the UV absorber containing solution is fed to thevessel holding the dope, and they are mixed. The mixture (dope) is fedto a casting head appropriately through a filter for the dope, and iscast from the casting head on a drum or continuous belt of metal(support). The cast film is dried during one rotation of the support toform a film having self-bearing properties, and the dried film isseparated from the support, and then the film is sufficiently dried tobe wound on a roll. In another embodiment the film may be dried in itsentirety and wound on the casting support as described in copendingcommonly assigned US patent application publication 2003/0215582A1, theteachings of which are incorporated herein by reference.

The dope and the absorber containing solution can be mixed by the use ofa static mixer which is mounted in the piping before the casting head,fed to the casting head and cast from the casting head on a metal drum(support). Any solvent can be employed in the solvent casting method solong as the polymer used (e.g., cellulose triacetate) can be dissolved.The solvent may be single solvent or a combination of solvents. Examplesof solvents employed in the solvent casting method include aliphatichydrocarbons such as pentane, hexane, heptane, octane, isooctane andcyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene;chlorinated hydrocarbons such as chloromethane, dichloromethane, carbontetrachloride and trichloroethane; alcohols such as methanol, ethanol,isopropyl alcohol and n-butyl alcohol; ketones such as acetone, methylethyl ketone, and cyclohexanone, and esters such as methyl formate,ethyl formate, methyl acetate and ethyl acetate, or dioxalane.

In the case of employing cellulose triacetate as the polymer, a mixedsolvent of dichloromethane and methanol is preferred. Other solventssuch as isopropyl alcohol and n-butyl alcohol can be employed so long ascellulose triacetate is not deposited (e.g., during the procedure ofpreparing the dope or adding particles to the dope). A ratio ofcellulose triacetate and solvent in the dope is preferably 10:90 to30:70 by weight (cellulose triacetate:solvent).

In the procedure of preparing the dope or the dispersion, variousadditives such as a dispersing agent, a fluorescent dye, an antifoamant,a lubricant, an antioxidant, a radical scavenger, an acid scavenger, aninhibitor of fade, and a preservative can be added to the dope or thedispersion. In addition, enhanced durability of the protectivelamination film to the action of light, heat, moisture, and oxygen interms of UV light blockage, visible spectrum color, and dimensionalstability may be imparted by the addition of chemical stabilizers fromthe list of hindered amine light stabilizers, hindered phenols, acidscavengers, and UV stabilizers. Combinations of stabilizer technologiesmay be employed as disclosed in commonly assigned US patent U.S. Pat.No. 6,767,937B2 and incorporated by reference herein.

Various functional layers such as a hard-coat layer, an anti-glarelayer, a low reflection layer, an anti-reflection layer, an anti-stainlayer, an anti-static layer, a conductive layer, an opticallyanisotropic layer, a liquid crystalline layer, an orientation layer, anadhesion layer, and a subbing layer can be provided on the polymer filmof the invention. These functional layers can be provided byconventionally known methods of coating, evaporation, sputtering, plasmadischarge, or flame discharge. A polarizer plate comprising saidfunctional layers then comprises an integral multilayer film structurecomprising the inventive polymer film claimed herein.

In a preferred embodiment, the protective film is employed in theproduction of polarizing plates, which polarizing plate comprises apolarizing film and, on one side or both sides of the polarizing film,the protective film.

The polarizing film can be prepared on commercial scale processingequipment designed for the production of display grade polarizers, forexample as described in U.S. Pat. No. 5,310,509A, hereby incorporatedherein by reference. In Example 1, polyvinyl alcohol (PVA) film is dyedwith a mixture of organic dichroic dyes and uniaxially stretched.Alternatively, as described in US 20020162483A1, hereby incorporatedherein by reference, particularly Section 0224, polyvinyl alcohol (PVA)film can be swollen in water, uniaxially stretched, and dyed withaqueous iodide. The polarizing film is then further immersed in anaqueous solution of boric acid, washed with water, and dried.

The polarizing plate, according to one particular embodiment, can beprepared as follows. The protective film, optionally combined, in amultilayer structure or composite film, with a carrier or otherfunctional films, can be laminated to polarizing film using a variety ofadhesives suitable for producing an optically uniform laminatedstructure. For example, cellulose triacetate film can be surfacehydrolyzed by immersion in aqueous base (such as 2 N NaOH) at elevatedtemperature (e.g., 60° C.), then washed with water, neutralized inaqueous mineral acid (such as 10% wt HCl), again washed with water, anddried. Adhesion of surface hydrolyzed cellulose triacetate can bepromoted by the use of aqueous PVA solution added to the nip of alamination process when sheets of surface hydrolyzed cellulosetriacetate are brought together on one or both sides of a PVA polarizingfilm. The resulting laminated polarizing plate is then dried to removeexcess internal moisture.

In the case where the protective film is combined in a multilayerstructure or composite film, with a carrier or other functional films,the protective film is preferably the self-bearing layer closest to thepolarizing film. However, in such cases, a tie-layer or bonding layer ofless than 5 microns may be present between the polarizing film and theprotective film.

The following examples are meant to be illustrative, but are notintended to be limiting in the choice of materials within the scope ofthe invention as should be obvious to those skilled in the art.

EXAMPLES Preparation of cyclohexane-1,2-dicarboxylic acid dihexyl ester

A mixture of 1,2-cyclohexanedicarboxylic anhydride (60 g), hexanol (85g), and p-toluenesulfonic acid (100 mg) in toluene (500 mL) was refluxedfor 3 days and water removed from the reaction mixture. After reactionwas complete, solvent was removed in vacuo to yield a viscous oil. Thecrude material was redissolved in heptane and passed through a pad ofsilica gel to obtain cyclohexane-1,2-dicarboxylic acid dihexyl ester (80g) as a pale yellow oil.

Preparation of 1,2,3-propanetricarboxylic acid tricyclohexyl ester

A mixture of 1,2,3-propanetricarboxylic acid (25 g), cyclohexanol (55g), and p-toluenesulfonic acid (100 mg) in toluene (500 mL) was refluxedfor 2 days and water removed from the reaction mixture. After reactionwas complete, solvent was removed in vacuuo to yield a viscous oil. Thecrude material was redissolved in heptane and passed through a pad ofsilica gel to obtain 1,2,3-propanetricarboxylic acid tricyclohexyl ester(50 g) as a pale yellow oil.

Preparation of cyclohexane-1,2-dicarboxylic acid, monoethyl ester,monohexadecyl ester

A mixture of 1,2-cyclohexanedicarboxylic acid monohexadecyl ester (whitesolid m.p.=54-55° C.) (8 g) (prepared from 1,2-cyclohexanedicarboxylicanhydride (1 eq), hexadecanol (1 eq), triethylamine (1 eq), in ethylacetate at room temperature for 24 hours) in 50 ml of tetrahydrofuranwas treated with oxalyl choloride (5 g) overnight at room temperature.After solvent removal in vacuuo the resultant acid chloride wasdissolved in 50 ml of absolute ethanol, and sodium carbonate (2.2 g) wasadded. The mixture was stirred for 3 hours, filtered and concentrated invacuuo. The light yellow liquid product was dissolved in hexane andpassed through a pad of silica gel. Solvent removal gavecyclohexane-1,2-dicarboxylic acid monoethyl ester monohexadecyl ester(5.3 g) as a clear colorless liquid which forms a waxy solid when cooledto below room temperature.

Testing of Acidic Hydrolysis Products:

A comparison of the reactivity of acidic hydrolysis products of esterplasticizers toward dichroic organic dyes was evaluated for a series ofcompounds. Acid compounds were selected as representative of potentialhydrolysis products of compounds described in the current invention, aswell as those disclosed in US 20020192397A1, US 20020162483A1, and US20030037703A1, each incorporated by reference. This experiment simulateshow, under environmental exposure to elevated temperature and humidity,plasticizers used in the protective films for polarizer plates have thepotential to degrade resulting in the release of reactive species.

For each acid compound a 5 millimolar solution was prepared using amixture of 1:1 DMSO:water solution containing 0.04 mg/mL of arepresentative dichroic dye compound described above (CAS Number121227-50-7). Periodic time aliquots of the solutions were evaluated byHPLC as described below to determine the loss of the dichroic dyecompound as the solution was held at 100° C. for 24 hrs. HPLC analysiswas performed on a YMC-AQ-302 column at 2.0 mL/min, 0.1 M sodium acetate(1:1 methanol:acetonitrile) mobile phase using 50 μL injections of theexperimental solutions with analyte detection at 640 nm. Table 1 belowsummarizes the resulting observed loss of CAS Number 121227-50-7dichroic dye upon exposure to acidic compounds.

TABLE 1 Percent loss of No. Acid Hydrolysis Product Dye 1 diphenylphosphate −83% 2 phthalic acid −38% 3 benzoic acid −18% 41,2-cyclohexane dicarboxylic acid −10% 5 tricarballylic acid −10%

Acid hydrolysis product 4 is a potential degradation product associatedwith Plasticizer Compounds 1-26 (above) usable in the present invention.Acid hydrolysis product 5 is associated with Plasticizer Compound 53.Acid hydrolysis products 1 to 3 are associated with plasticizercompounds other than the plasticizer compounds required by the presentinvention.

The results shown in Table 1 above clearly indicate that acidiccompounds corresponding to compounds described for use in the presentinvention show minimal loss of dichroic dye. Conversely, acidiccompounds released by hydrolysis of various other ester plasticizercompounds produce significant loss in dichroic dye.

Evaluation of Protective Lamination Films:

Example 1A:

In a mixing vessel for a polymer dope, 100 weight parts of cellulosetriacetate (TAC) (combined acetic acid value: 60.8%), 11.24 weight partsof a plasticizer compound 1, 0.107 weight parts of Parsol® 1789(4-(1,1-dimethylethyl)-4′-methoxydibenzoylmethane), 0.91 weight partsTinuvin® 328 (2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole),0.16 weight parts Tinuvin® 326(2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole),405 weight parts of dichloromethane, and 45.0 weight parts of methanolwere placed, and all components were dissolved by stirring under heatingto prepare a dope.

The mixed dope was fed to an extrusion die and cast on a moving metalsupport. After the cast film was separated from the casting surface, thefilm was dried by passing through a heating zone to prepare a celluloseacetate film having a thickness of 80 μm providing a polymer filmsuitable for the protective lamination film component of a polarizingplate.

Examples 1B and 1C

All parts of preparing the dope and protective lamination film were asdescribed in Example 1A with the exception that for Ex. 1B, 5.62 weightparts of a plasticizer compound 1 was used and for Ex. 1C, 16.86 weightparts of a plasticizer compound 1 was used.

Example 2A, 2B and 2C

A polymer dope was prepared as in Example 1A with the exception thatdifferent weight parts of a plasticizer compound 53 were used in placeof the compound 1 as follows; Ex. 2B, 5.62; Ex. 2A, 11.24; and Ex 2C,16.86 weight parts of compound 53. All other parts of preparing the dopeand the protective lamination film were as described in Example 1A.

Example 3

A polymer dope was prepared as in Example 1A with the exception that11.24 weight parts of a plasticizer compound 53 was used in place of thecompound 1 and 0.56 weight parts of poly(4-vinyl pyridine) was added tothe dope. All other parts of preparing the dope and the protectivelamination film were as described in Example 1A.

Comparative Example 1A, 1B, and 1C

A polymer dope was prepared as in Example 1A with the exception thatdifferent weight parts of triphenyl phosphate were used in place of thecompound 1 as follows: Comp. Ex. 1B, 5.62; Comp. Ex. 1A, 11.24; andComp. Ex. 1C, 16.86 weight parts of triphenyl phosphate. All other partsof preparing the dope and the protective lamination film were asdescribed in Example 1A.

Comparative Example 2

A polymer dope was prepared as in Example 1A with the exception that11.24 weight parts of triphenyl phosphate was used in place of thecompound 1 and 0.56 weight parts of poly(4-vinyl pyridine) was added tothe dope. All other parts of preparing the dope and the protectivelamination film were as described in Example 1A.

Comparative Example 2

A polymer dope was prepared as in Example 1A with the exception that aplasticizer compound was not used. All other parts of preparing the dopeand the protective lamination film were as described in Example 1A.

Protective Lamination Film Performance:

For the example protective lamination films, the compatibility of theplasticizer with the polarizer plate lamination was evaluated. Inparticular, the tendency of plasticizers to migrate to the protectivelamination film surface strongly affects the adhesion quality to thepolarizing film. Plasticizer surface excess concentration was evaluatedby ATR-FTIR using a BioRad® FTS 60 FTIR Spectrophotometer with a SpecacGolden Gate® ATR Accessory. Table 2 below shows the observed trends insurface excess plasticizer (or deficit as indicated by a negativenumber) in the top 1.2 microns of the film. Reduced surface excess isindicative of improved compatibility of the plasticizer with the polymerfilm.

TABLE 2 Ex. A Ex. B Ex. C 5% Wt 10% Wt 15% Wt plasticizer in plasticizerin plasticizer in film film film Example Com- 0.3% surface −3.5% surface−0.9% surface set 1 pound 1 excess excess excess Example Com- −0.3%surface −3.8% surface −5.3% surface set 2 pound 53 excess excess excessCom- triphenyl 1.6% surface 4.2% surface 7.1% surface parative phosphateexcess excess excess Example set 1

The results shown in Table 2 clearly indicate that a significantimprovement in plasticizer compatibility with the protective film isprovided through the incorporation of the non-aryl ester compounds usedin the present invention as compared with the commonly used triphenylphosphate.

Protective Film Performance (Contact Angle):

As described above, each example protective film was prepared forlamination to the polarizing film by alkaline surface hydrolysis. Thequality and uniformity of the subsequent adhesion between the surfacehydrolyzed protective film and the polarizing film is determined by thesurface energy of the films. Water contact angle is employed as a directindication of surface energy. Accordingly, a higher water contact angleis indicative of a lower surface energy that can tend to be relativelyadverse for adhesion quality.

To promote effective adhesion to the PVA polarizing film, a watercontact angle of less than 35° is desirable. In addition, to promoteuniform adhesion, a uniform surface energy (uniform water contact angle)is obviously desirable. Table 3 below shows the advancing water contactangle of alkaline hydrolyzed example films measured after 120 secondsfor each example protective lamination film both freshly afterhydrolysis and 11 days after hydrolysis stored at 25° C., 50% RH.

TABLE 3 Freshly 11 days after film hydrolyzed film surface hydrolysisPlasticizer Mean Std Dev Mean Std Dev Example 1A Compound 1 20.2° 3.3°28.3° 6.1° Example 2A Compound 53 24.7° 1.1° 28.0° 6.8° Comparativetriphenyl 16.7° 1.4° 44.7° 12.0° Example 1A phosphate

The results shown in Table 3 clearly indicate that the incorporation ofthe non-aryl ester compounds used in the present invention provide low,stable and uniform surface energy of the protective film after surfacehydrolysis. On the contrary, the commonly used triphenyl phosphate showsboth significant non-uniformity and a dramatic increase in surfaceenergy to a level that would compromise adhesion with time after surfacehydrolysis. These results are consistent with the enhanced compatibilityof the inventive non-aryl ester compounds as protective filmplasticizers. These results are consistent with the relatively lowertendency of the plasticizer compounds used in the present invention tosurface segregate as demonstrated in Table 2 above.

Polarizer Plate Durability:

Each example polarizer plate was evaluated for environmental durabilityby storage at 80° C., 90% relative humidity. The polarizer plates wereevaluated periodically for retention of their polarization efficiencyand light transmission performance for up to 1400 hours. Determinationof the CIE human perception photopic transmission (Y value) was madeusing the D65 illumination (1964 observer) standard. Polarizationefficiency was calculated as shown in the following Equation 1:PE=100[(Y _(∥) −Y _(⊥))/(Y _(∥) +Y _(⊥))]^(1/2)  (Eq. 1)

Dichroic-dye PVA polarizing films were prepared having been dyed with amixture of Direct Orange 39, Direct Red 81, Direct Violet 9, and DirectBlue 98 to obtain a neutral hue. Each example protective lamination filmafter alkaline hydrolysis was used to prepare polarizer plates bylamination to both sides of the polarizing film using anaqueous:methanol:PVA glue in the lamination nip. For environmentaldurability testing, polarizer plates were dried and adhered to Corning®Type 1737-G glass using an optical grade pressure sensitive adhesive.Table 4 below shows the change in dichroic organic dye polarizer platePolarization Efficiency, PE, and Photopic Transmission, Y, afterexposure to 80° C., 90% RH conditions.

TABLE 4 Time Low mobility Time till till |5%| basic 5% Loss Change inSample Plasticizer compound in PE (hr) Y (hr) Example 1A Compound 1None >1400 >1400 Example 2A Compound 53 None 1200 1400 Example 3Compound 53 poly(4-vinyl >1400 >1400 pyridine) Comp. Ex. 1A triphenylNone 440 630 phosphate Comp. Ex. 2 triphenyl poly(4-vinyl 800 770phosphate pyridine)

The results shown in Table 4 above clearly indicate that a significantimprovement in dichroic-dye polarizer plate durability is providedthrough the incorporation of the inventive non-aromatic ester compoundsin the protective lamination films applied to the polarizer plate. Incontrast, commonly used triphenyl phosphate is associated with rapidfailure of the polarizer plate performance. Significant improvement isdemonstrated by the addition of an oligomeric or polymeric low mobilitybasic compound.

Iodine-dyed polarizing films were prepared having been dyed with anaqueous KI and I₂ solution after uniaxial stretching. Each exampleprotective lamination film after alkaline hydrolysis was used to preparepolarizer plates by lamination to both sides of the polarizing filmusing an aqueous:methanol:PVA glue in the lamination nip. Forenvironmental durability testing, polarizer plates were dried andadhered to Corning® Type 1737-G glass using an optical grade pressuresensitive adhesive. Table 5 below shows the change in iodine dyedpolarizer plate Polarization Efficiency, PE, and Photopic Transmission,Y, after exposure to 80° C., 90% RH conditions, relative to bestperformance.

TABLE 5 Time till 5% Time till 5% Change in Y Sample Plasticizer Loss inPE (hr) (hr) Example 1A Compound 1 >1000 >1000 Example 2A Compound 53570 640 Comp. Ex. 1A triphenyl phosphate 520 510 (hazy) Comp. Ex. 3 None200 500

The results shown in the above Table 5 clearly indicate that asignificant improvement in iodine dyed polarizer plate durability isprovided through the incorporation of the inventive non-aromatic estercompounds in the protective lamination films applied to the polarizerplate. In contrast, protective films with either no plasticizer or thecommonly used triphenyl phosphate are associated with more rapid failureof the polarizer plate performance.

Parts List

-   10 protective polymer films-   20 polarizing film

1. A self-bearing polymer film comprising a polymer selected fromcellulose esters, polycarbonate esters, and norbornene resins, whichpolymer film comprises, in a polymer phase, at least one plasticizercompound represented by the following structure:

wherein: R¹ and R² are both non-aryl groups at the bond to the —C(═O)O—ester link; n is an integer of 2 or more, wherein each R² may be thesame or different; and at least one cycloalkyl group is present ineither or both of R¹ and R², wherein the cycloalkyl group is acyclohexyl or cyclopentyl group; wherein the self-bearing polymer filmhas mechanical, optical, and chemical properties for use as a protectivelayer disposed on one or both sides of a polarizing film to form apolarizing plate, the self-bearing polymer film having a thicknessranging from 5 to 200 microns, exhibiting an in-plane retardationranging from 0.1 to 15 nm, an out-of-plane retardation ranging from −10to −100 nm, and wherein the plasticizer compound is present in the rangeof about 1 to 30 weight percent.
 2. The self-bearing film of claim 1wherein R² and R¹ are, respectively, the residues resulting from thereaction product of an alcohol and carboxylic acid.
 3. The self-bearingfilm of claim 1 wherein the non-aryl groups R¹ and R² may be selectedfrom alkyl, alkenyl, alkynyl, cycloalkyl, and cycloalkenyl, which groupsmay be substituted or unsubstituted and heteroatoms may be present aspart of the chemical structure of R¹ or R^(2,) but any heteroatoms arenot directly bonded to the carbonyl carbon or oxy of the ester link. 4.The self-bearing film of claim 1 there are no aromatic groups present aspart of R¹ and R², unless the aromatic group is not directly bonded tothe carbonyl carbon or oxy of the ester link.
 5. The self-bearing filmof claim 1 wherein optional substituents on R¹ and R² are independentlyselected from a phenyl group, an alkyl group, an alkoxy, a hydroxy, ahalogen group, an alkyl ether group, an alkyl thioether group, or aheterocyclic group.
 6. The self-bearing film of claim 1 wherein R¹ is acyclohexyl, cyclopentyl, alkyl cyclohexyl, or alkyl cyclopentyl group.7. The self-bearing film of claim 6 where at least two R² groups areindependently a cycloalkyl group or alkyl cycloalkyl.
 8. Theself-bearing film of claim 1 wherein at least one R² is a cycloalkylgroup or alkyl cycloalkyl, and R¹ is not a cycloalkyl.
 9. Theself-bearing film of claim 1 wherein at least one R² group and the R¹group are independently a cycloalkyl group or an alkyl cycloalkyl group.10. The self-bearing film as in claim 1 wherein the plasticizer compoundis derived from a cycloalkyl polycarboxylic acid containing two or morecarboxylate residues each forming an ester linkage to a residue of amonohydric alcohol.
 11. The self-bearing film of claim 10 wherein thecycloalkyl polycarboxylic acid is a cyclohexyl polycarboxylic acidcontaining two or more carboxylate residues each forming an esterlinkage to a residue of a monohydric alcohol.
 12. The self-bearing filmof claim 10 wherein each monohydric alcohol is a linear chain, branchedor cyclic alkyl monohydric alcohols containing 3 to 16 carbon atoms. 13.The polymer film as in claim 12 wherein at least one monohydric alcoholis a linear chain, branched or cyclic alkyl monohydric alcoholscontaining six carbon atoms.
 14. The self-bearing film of claim 1wherein the plasticizer compound is a reaction product of apolycarboxylic acid having pKa greater than
 3. 15. The self-bearing filmof claim 1 wherein the polymer phase comprise a polymer selected frompolyesters, cellulose esters, polyolefins, acrylic resins, polycarbonateesters, or norbornene resins.
 16. The self-bearing film of claim 15wherein the polymer is selected from polyethylene terephthalate,polyethylene-2,6-naphthalate, cellulose diacetate, cellulose triacetate,cellulose acetate propionate, cellulose acetate butyrate, polypropylene,polyethylene, polymethyl methacrylate, bisphenol-A-polycarbonate,bisphenol-A-trimethylcyclohexane-polycarbonate,bisphenol-A-phthalate-polycarbonate, and norbornene resins.
 17. Theself-bearing film of claim 1 wherein the polymer is selected fromcellulose diacetate, cellulose triacetate, cellulose acetate propionate,cellulose acetate butyrate, bisphenol-A-polycarbonate,bisphenol-A-trimethylcyclohexane-polycarbonate,bisphenol-A-phthalate-polycarbonate, and norbornene resins.
 18. Theself-bearing film of claim 1 wherein the polymer is a cellulose ester.19. The self-bearing film of claim 18 wherein the polymer is celluloseacetate.
 20. The self-bearing film of claim 1 wherein the plasticizercompound is present in the range of about 5 to 15 weight percent. 21.The self-bearing film of claim 1 further comprising a plasticizercompound selected from phosphate esters, phthalate esters, or glycolicacid esters.
 22. The self-bearing polymer film as in claim 1 furthercomprising an oligomeric or polymeric low-mobility basic compound. 23.The self-bearing polymer film of claim 22 wherein the low-mobility basiccompound is selected from: poly(4-vinylpyridine), poly(2-vinylpyridine),poly(acrylonitrile-co-butadiene)(amine terminated), poly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine],poly(1,2-dihydro-2,2,4-trimethylquinoline), polyethyleneimine,polyethyleneimine (epichlorohydrin modified), polyethylenimine (80%ethoxylated), poly(9-vinylcarbazole), poly(vinylchloride-co-1-methyl-4-vinylpiperiazine), andpoly(4-vinylpyridine-co-butyl methacrylate).
 24. A polarizer platecomprising an integral multilayer film structure that comprises a layerof a light polarizing material and at least one self-bearing filmaccording to claim 1, wherein there are no aryl groups bonded directlyto either side of all ester linkages in said plasticizer compound. 25.The polarizer plate of claim 24 wherein the layer of light polarizingmaterial is located between two of said self-bearing films.
 26. Thepolarizer plate of claim 24 wherein the light polarizing materialcomprises one or more dichroic organic dyes.
 27. The polarizer plate ofclaim 24 wherein the light polarizing material comprises iodine.
 28. Adisplay device comprising a polarizer plate comprising at least oneself-bearing film of claim 1 and a layer of a light polarizing materialin an integral multilayer film structure.
 29. The display device ofclaim 28 wherein the display device is a liquid crystal display or anelectroluminescent display device.
 30. A self-bearing polymer filmcomprising a polymer selected from cellulose esters, polycarbonateesters, and norbornene resins, and at least one plasticizer compoundrepresented by the following structure:

wherein: R¹ and R² are both non-aryl groups at the bond to the —C(═O)O—ester link; n is an integer of 2 or more, wherein each R² may be thesame or different; and one or more cycloalkyl groups are present ineither or both R¹ and R², wherein the cycloalkyl group is a cyclohexylor cyclopentyl group; wherein the self-bearing polymer film hasmechanical, optical, and chemical properties for use as a protectivelayer disposed on one or both sides of a polarizing film to form apolarizing plate, the self-bearing polymer film having a thicknessranging from 5 to 200 microns, exhibiting an in-plane retardationranging from 0.1 to 15 nm, an out-of-plane retardation ranging from −10to −100 nm, and wherein the plasticizer compound is Present in the rangeof about 1 to 30 weight percent; the self-bearing polymer film furthercomprising a functional layer selected from the group consisting of ananti-glare layer, a low reflection layer, an anti-reflection layer, anoptically anisotropic layer, and a liquid crystalline layer.
 31. Acomposite film comprising a carrier substrate and a self-bearing polymerfilm, comprising a polymer selected from cellulose esters, polycarbonateesters, and norbornene resins, which polymer film comprises, in apolymer phase, at least one plasticizer compound represented by thefollowing structure:

wherein: R¹ and R² are both non-aryl groups at the bond to the —C(═O)O—ester link; n is an integer of 2 or more, wherein each R² may be thesame or different; and either or both the R¹ and R² comprise at leastone cycloalkyl group wherein the cycloalkyl group is a cyclohexyl orcyclopentyl group, wherein the self-bearing polymer film has mechanical,optical, and chemical properties for use as a protective layer disposedon one or both sides of a polarizing film to form a polarizing plate,the self-bearing polymer film having a thickness ranging from 5 to 200microns, exhibiting an in-plane retardation ranging from 0.1 to 15 nm,an out-of-plane retardation ranging from −10 to −100 nm, and wherein theplasticizer compound is present in the range of about 1 to 30 weightpercent.